<template>
	<scroll 
	      class="listview" 
	      ref="listview"
		  :listenScroll="listenScroll"
		  @scroll="scroll"
		  :probe-type="probeType"
	      >
		<ul>
			<li  v-for="group in data"
			     class="list-group"
			     ref="listGroup"
			>
				<h2 class="list-group-title">{{group.title}}</h2>
				<ul>
					<li v-for="item in group.items"
					    class="list-group-item"
						 @click="selectItem(item)"
					    >
						<img class="avatar" v-lazy="item.avatar">
						<span class="name">{{item.name}}</span>
					</li>
				</ul>
			</li>
		</ul>
        <div class="list-shortcut"
             @touchstart='onShortcutTouchStart'
             @touchmove.stop.prevent="onShortcutTouchMove">
        	<ul>
        		<li 
        		    v-for='(item,index) in shortcutList'
        		    class="item"
        		    :data-index="index"
        		    :class='{"current":currentIndex===index}'
        		    >
        		    {{item}}
        	   </li>
        	</ul>
        </div>
        <div class="list-fixed" v-show="fixedTitle" ref="fixed">
        	<h1 class="fixed-title">{{fixedTitle}}</h1>
        </div>
        <div v-show='!data.length' class="loading-container">
        	<loading></loading>
        </div>
	</scroll>
</template>

 <script>
 import scroll from 'base/scroll/scroll'
 import loading from'base/loading/loading'
 import {getData} from 'common/js/dom'
 const ANCHOR_HEIGHT = 18
 const TITLE_HEIGHT = 30
 export default {
 	name: "ListView",
 	created () {
 		this.touch = {}
 		this.listenScroll= true
 		this.listHeight= []
 		this.probeType = 3
 	},
 	props: {
 		data: {
 			type: Array,
 			default: [],
 		}
 	},
 	data () {
 		return{
 			scrollY: -1,
 			currentIndex: 0,
 			diff: -1
 		}
 	},
 	components: {
 		scroll,
 		loading
 	},
 	computed: {
 		shortcutList() {
 			return this.data.map((group)=>{
 				return group.title.substr(0,1)
 			})
 		},
 		fixedTitle(){
 			if(this.scrollY>0){
 				return  ''
 			}
 			return this.data[this.currentIndex] ? this.data[this.currentIndex].title:''
 		}
 	},
 	methods: {
 		selectItem(item) {
 			this.$emit('select',item)
 		},
 		onShortcutTouchStart(e) {
 			let anchorIndex = getData(e.target,'index')
 			let firstTouch= e.touches[0]
 			this.touch.y1= firstTouch.pageY
 			this.touch.anchorIndex=anchorIndex
 			this._scrollTo(anchorIndex)
 		},
 		onShortcutTouchMove(e) {
 			let firstTouch=e.touches[0]
 			this.touch.y2=firstTouch.pageY
 			let delta=(this.touch.y2-this.touch.y1)/ANCHOR_HEIGHT | 0
 			let anchorIndex=parseInt(this.touch.anchorIndex)+delta
 			this._scrollTo(anchorIndex)
 		},
    refresh() {
        this.$refs.listview.refresh()
    },
 		scroll(pos) {
 			this.scrollY=pos.y
 		},
 		_scrollTo(index) {
 			if(index === null){
 				return
 			}
 			if(index<0) {
 				index=0
 			}else if (index > this.listHeight.length-2){
 				index = this.listHeight.length -2
 			}
 			this.scrollY = -this.listHeight[index]
 			this.$refs.listview.scrollToElement(this.$refs.listGroup[index],0)
 		},
 		_calculateHeight() {
 			this.listHeight = []
 			const list= this.$refs.listGroup
 			let height= 0
 			this.listHeight.push(height)
 			for(let i = 0; i < list.length; i++) {
 				let item=list[i]
 				height+=item.clientHeight
 				this.listHeight.push(height)
 			}
 		}
 	},
 	watch: {
 		data() {
 			setTimeout(()=>{
 				this._calculateHeight()
 			},20)
 		},
 		scrollY(newY) {
 			const listHeight = this.listHeight
 			if(newY > 0){
 				this.currentIndex = 0
 				return
 			}
 			for( let i=0;i<listHeight.length-1;i++) {
 				let height1 = listHeight[i]
 				let height2 = listHeight[i+1]
 				if(-newY >= height1 && -newY<height2) {
 					this.currentIndex = i
 					this.diff=height2+newY
 					return
 				}
 			}

 			this.currentIndex = listHeight.length-2
 		},
 		diff(newVal) {
 			let fixedTop = (newVal>0 && newVal<TITLE_HEIGHT)?newVal-TITLE_HEIGHT:0
 			if(this.fixedTop === fixedTop){
 				return
 			}
 			this.fixedTop = fixedTop
 			this.$refs.fixed.style.transform=`translate3d(0,${fixedTop}px,0)`
 		}
 	}
 	
 }	
 </script>
<style scoped lang="stylus" rel="stylesheet/stylus">
  @import "~common/stylus/variable"
  .listview
    position: absolute
    width: 100%
    height: 100%
    overflow: hidden
    background: $color-background
    .list-group
      padding-bottom: 30px
      .list-group-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
      .list-group-item
        display: flex
        align-items: center
        padding: 20px 0 0 30px
        .avatar
          width: 50px
          height: 50px
          border-radius: 50%
        .name
          margin-left: 20px
          color: $color-text-l
          font-size: $font-size-medium
    .list-shortcut
      position: absolute
      z-index: 30
      right: 0
      top: 50%
      transform: translateY(-50%)
      width: 20px
      padding: 20px 0
      border-radius: 10px
      text-align: center
      background: $color-background-d
      font-family: Helvetica
      .item
        padding: 3px
        line-height: 1
        color: $color-text-l
        font-size: $font-size-small
        &.current
          color: $color-theme
    .list-fixed
      position: absolute
      top: 0
      left: 0
      width: 100%
      .fixed-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
    .loading-container
      position: absolute
      width: 100%
      top: 20%
      transform: translateY(-50%)
</style>
